1. Field of the Invention
This invention relates to a gas generator for an air bag for protecting a passenger from impact, and more particularly, to a novel housing structure for a gas generator.
2. Prior Art
A conventional housing structure for a gas generator for air bags is disclosed in U.S. Pat. No. 4,547,342. This structure includes a housing comprising a diffuser shell and a closure shell. The diffuser shell is molded by forging, and has three concentric cylinders: an ignition chamber, a combustion chamber formed outside the ignition chamber and a coolant/filter chamber formed outside the combustion chamber. An opening for mutually communicating the combustion and coolant/filter chambers is bored in the cylinder and a gas discharge port is bored in the outer cylinder. The diffuser shell and the closure shell are bonded to each other by three concentric weld portions formed by friction welding. Ignition means, i.e. an igniter, is fitted into the inner cylinder of the closure shell and welding takes place while the igniter 53 is in the hole.
Various other prior art references, similarly, include means for fastening the diffuser shell to the closure shell in ways that add to the size and weight of the gas generator. Such references are as follows:
U.S. Pat. No. 3,532,360 to Leising, et al, discloses a gas generating apparatus having a housing, a gas generating section, a coolant chamber, and inflatable air bag. The housing is generally bowl shaped and includes a bottom wall and a side wall. The gas generator is separated from an air bag by a plate having holes extending therethrough and a diaphragm which ruptures under pressure when the gas generant begins burning. The burning mixture is propelled into the air bag and continues to burn to achieve full inflation of the bag.
U.S. Pat. No. 3,618,980 to Leising, et al, discloses a gas generator having an ignitable propellant and a bag adapted to be inflated by gas released from the propellant. Also included is a trapping device for inhibiting movement of burning propellant from the gas generator to the interior of the bag. The trapping device includes a deflector which directs the propellant toward veins. The veins direct the materials towards the walls of the chamber in which they are positioned, causing the materials to travel in a generally circular pass, thereby enhancing combustion of the propellant. Because of their mass and velocity, reacting particles are kept in the chamber until fully consumed. A gas generator is contained in two housings that are connected together by plurality of fasteners.
U.S. Pat. No. 3,632,133 to Hass, discloses an inflatable air bag that includes a gas generator which, upon ignition, produces a high velocity gas stream directed into the converging end of a converging-diverging nozzle and then into the inflatable air bag. The high velocity stream of gas also influences the drawing of gas from the exterior of the gas generator into the air bag.
U.S. Pat. No. 3,985,076 to Schneiter et al, discloses a gas generator having an inner housing and an outer housing forming an annular chamber, having a central ignition means surrounded by a gas generant composition. The inner housing has a plurality of peripheral orifices. The inner housing is threadably engaged with the outer housing. The gas generant is surrounded by a diaphragm which is ruptured upon ignition. The resulting gases are then passed through a filter for solid particles, then through a pH neutralizing material and cooling device before being expelled into an inflatable structure.
U.S. Pat. No. 4,296,084 to Adams et al, discloses a method and apparatus for gas generation comprising a housing comprising an upper convex half shell threadably attached to a lower concave half shell. Within the housing is a combustion chamber having a gas generant, an igniter, a primary filter means in the combustion chamber comprised of a woven fabric which swells and becomes tacky at the temperature of the combustion process to retard the outflow from the combustion chamber of combustible products, and a secondary filter located outside of the combustion chamber.
U.S. Pat. No. 4,278,638 to Nilsson, et al, discloses a gas generator construction having a housing with a central tubular housing part which contains an ignition device, surrounded by a reaction chamber containing a gas generant, surrounded by a filter. The device includes a S-shaped wall member forming part of the reaction chamber, having an aperture through which gases flow to the expansion chamber.
U.S. Pat. No. 4,530,516 to Adams, et al, discloses a gas generator for use with an inflatable air bag comprising an upper shell and a lower shell welded together and an elongated steel center-tie member rigidly attached through the center of the housing having a hollow cylindrical perforated body containing an igniter charge assembly. Surrounding the center-tie member is an annular chamber containing a gas generant. After combustion of the gas generant, gases flow circumferentially through a screen filter and through a diffuser screen assembly, through exit ports of the housing into the air bag.
U.S. Pat. No. 4,547,342 to Adams, et al, discloses a gas generator for use with an inflatable air bag comprising a housing having an upper shell and a lower shell welded together. Within the housing are three integrally formed concentric cylinders defining chambers. A gas generant is contained in the combustion chamber. Upon ignition of the gas generant, gases flow through an inner screen filter pack radially outward through a combustion chamber exit where they are turned downward by a deflector ring where they strike flashing and then flow radially outward between the deflector ring and an outer screen pack, through the outer screen pack and finally exit port holes in the housing.
U.S. Pat. No. 4,578,247 to Bolleau, discloses a gas generator comprising a housing having two subassemblies each having first and second concentric cylinders joined together by welding to form an igniter chamber and an outer chamber. The outer chamber is divided into three axial chambers, the first of which contains a fuel and the second and third chambers cooling and filtering means.
U.S. Pat. No. 4,590,041 to Hill, discloses a gas generator wherein gas generant pellets are maintained under pressure to improve the duration stability and decrease the degradation of the gas generant pellets. Pressure is applied by a plate that is spring biased against the pellets.
U.S. Pat. No. 4,943,086 to Cunningham, discloses a gas generator having a housing comprising an inner shell welded to an outer shell. Within the housing defined by the shells is an inner combustion chamber in the outer diffuser chamber. The igniter material is contained within a container that is free of attachment to any structural component of the housing, thereby permitting a greater number of apertures to be provided therein or a more diffused pattern of gas flow into the combustion chamber. This eliminates the need for an ignition cup for the igniter powder as the squib may fire directly into the igniter powder and insure greater ignition thereof.
Japanese Patent No. JP 63-301144 to Mizoguchi, discloses a structure of an air bag comprising a lattice configuration or a multiple pillar-shaped configuration so that less air is required for inflation of the air bag.
Japanese Patent No. JP 47-30045 to Kogyo, discloses a rapidly inflatable apparatus for shock absorption comprised of a series of tube-like inflators linked together by a piece of material which accepts an accelerated body after a collision.
Japanese Patent No. JP 50-16057 to Toyota Motor Corporation, discloses an air bag having inner and outer films joined by blocked connecting portions which take on a lattice or wave-like shape to maintain the shape of the bag.
The conventional housing structures described in the prior art involve the following problems:
1. Since bonding is effected by friction welding, fins develop. Accordingly, and an excessive space is necessary to accommodate the fins. Particularly, the outside fins must be removed from the aspect of appearance, etc. When the fins are not removed, the peripheral wall portion of the closure shell is formed overlappingly with the peripheral wall portion of the diffuser shell in such a manner as to cover the fins. In this case, an excessive material is necessary in the amount corresponding to the overlapping portion, and the weight increases as much.
2. To accomplish sufficient friction welding, the weld portion of the closure shell must be shaped as concentric protuberances. A part of these protuberances remain even after friction welding, and a space thereby defined. Accordingly, unnecessary increases in weight and volume occur.
3. Since welding is carried out while ignition means containing an ignition powder is fitted, there is the problem of safety during production. Furthermore, explosion-proof installation must be provided as a safety measure.
4. Since two openings are disposed on the same axis from the aspect of boring, the arrangement structure of the coolant and the filter is limited.
5. Visual inspection of the weld portions is difficult. In other words, it is not easy to find weld defects because the weld portions cannot be inspected from outside the housing.
6. Boring to form a hole in the closure shell is necessary to fit the ignition means.
7. Both the diffuser and closure shells are shaped by forging. However, since they have three concentric cylinders, the surface of the round portion does not become flat, and cutting is necessary.
Accordingly, the present invention aims at providing a novel gas generator for an air bag which solves the problems associated with the prior art.